1. Field of the Invention
This invention relates to an electronic apparatus having a cooling unit for cooling a heat-generating component such as a semiconductor package.
2. Description of the Related Art
An electronic apparatus such as a portable computer contains a microprocessor for processing information. In microprocessors of this type, the consumption of power is being more and more increased in accordance with increases in processing speed or functionality, and the amount of heat generated is being increased proportionally. Accordingly, to maintain stable operation of the electronic apparatus, it is necessary to increase the degree of heat dissipation of the microprocessor.
To this end, a conventional electronic apparatus is equipped with a cooling unit using air for cooling its microprocessor. This cooling unit includes a heat sink for absorbing and dissipating the heat of the microprocessor, and an electromotive fan for supplying cooling air to the heat sink.
The heat sink has a heat-receiving section thermally connected to the microprocessor, radiator fins and cooling air passages for passing cooling air. The cooling air passages are formed along the heat-receiving section and radiator fins. The downstream ends of the cooling air passages oppose an exhaust port formed in a sidewall or the real wall of the housing.
The electromotive fan includes a fan casing with suction and discharge ports, and an impeller contained in the fan casing. The impeller draws air through the suction port, and discharges the drawn air into the cooling air passages through the discharge port. The discharged air serves as cooling air, and is heated by heat exchange with the heat sink while it is passing through the cooling air passages. The cooling air having absorbed the heat of the heat sink is discharged to the outside of the housing through the exhaust port.
In the conventional cooling unit, the cooling air passing through the cooling air passages is the main coolant for absorbing the heat of the microprocessor. Therefore, the greater part of the microprocessor-cooling performance depends upon the temperature difference between the cooling air and heat sink (microprocessor), and the amount of cooling air.
However, the heat of the microprocessor is discharged to the interior of the housing, as well as to the heat sink. Since the housing contains a plurality of circuit components such as a power supply unit that generates heat during operation, the air in the housing is heated by the microprocessor and circuit components. Therefore, the temperature difference between the heat sink and the air within the housing to be blown as cooling air onto the heat sink by the electromotive fan is small.
This means that the heat exchange between the cooling air and heat sink cannot be executed efficiently, thereby degrading the microprocessor-cooling performance.
To overcome this problem, a cooling unit has been recently available, which uses outside fresh air to cool the heat sink. In this cooling unit, a sufficient temperature difference can be secured between the cooling air and heat sink, which enhances the microprocessor-cooling performance.
Since, however, this cooling unit is used mainly to cool the microprocessor, it cannot positively draw and discharge the air within the housing. Accordingly, the interior of the housing is easily filled with the heat emitted from the other circuit components. Thus, the internal temperature of the housing is inevitably increased, which may cause the housing itself to become hot and require heat-resistant circuit components.